KATHMANDU (Reuters) - Floods triggered by incessant rains in Nepal have left thousands of people homeless, destroyed crops and disrupted transport and electricity supplies across the country, officials and media reports said on Friday.

Around 2,500 houses have been washed away in the Himalayan nation's southern plains, forcing residents to flee to higher grounds after week-long heavy rains, local media said.

Officials said floods and landslides have killed about 40 people in Nepal since June when the annual monsoon rains began.

"The seasonal monsoon trough lies almost parallel to the foot of the Himalayas causing more than normal rainfall in Nepal," said Shiva Nepal, an official at the weather forecasting office.

He said rain would continue for another two to three days.

In the western district of Sallyan, heavy rains caused a landslide, which swept away a home killing five members of a family while they were asleep on Thursday, Kantipur television reported.

Landslides and floods are common in Nepal during the monsoon season that continues through to September and often affect huge swathes of agricultural land in the mostly mountainous country.

The United Nations said on Thursday natural disasters in 2006 and 2007 had severely hurt crop production, leaving more than half of Nepal's 75 districts with food shortages.